Outer ring member for constant velocity joint and method of manufacturing the member

ABSTRACT

An outer ring member for a constant velocity joint is manufactured. An intermediate preformed product  16  having a cup section  21  with an incomplete shape is formed by pressing a large diameter section  14  without applying a low temperature annealing treatment and a lubricating chemical conversion coating treatment. Then, applying a low temperature annealing treatment and a lubricating chemical conversion coating treatment to the intermediate preformed product  16,  thereafter a formed product having a cup section  8  provided with ball-rolling grooves  17   a  to  17   f  is formed by backward extrusion to the intermediate preformed product  16.  Subsequently, the product is ironed before hardening, without applying a low temperature annealing treatment and a lubricating chemical conversion coating treatment to the formed product.

TECHNICAL FIELD

[0001] The present invention relates to an outer ring member for aconstant velocity joint and a method of manufacturing the member. Inparticular, the present invention relates to an outer ring member for aconstant velocity joint which can be manufactured efficiently, and amethod of manufacturing the member.

BACKGROUND ART

[0002]FIG. 10 shows a driving force transmission mechanism which iscarried on an automobile or the like and which is used to transmit thedriving force from an internal combustion engine to axles. In thedriving force transmission mechanism, outer ring members 1, 1 for abarfield-type constant velocity joint and outer ring members 2, 2 for atripod-type constant velocity joint are connected to one another byspline shafts 3, 3. A differential gearing 4 is interposed between theouter ring members 2, 2 for the tripod-type constant velocity joint.Both of the outer ring members 2, 2 for the tripod-type constantvelocity joint are arranged near the differential gearing 4. On theother hand, the outer ring members 1, 1 for the barfield-type constantvelocity joint function to transmit the rotary driving force tounillustrated wheels. In FIG. 10, reference numeral 5 indicates a halfshaft for bridging the differential gearing 4 and the outer ring member1 for the tripod-type constant velocity joint.

[0003] The end of the half shaft 5 is connected to the outer ring member1 for the barfield-type constant velocity joint by a plurality ofrollable balls 6.

[0004]FIG. 11 shows a schematic perspective view illustrating the entireouter ring member 1 for the barfield-type constant velocity joint, andFIG. 12 shows, with partial cutaway, a sectional view illustrating theouter ring member 1 for the barfield-type constant velocity joint. Theouter ring member 1 for the barfield-type constant velocity joint ismade of carbon steel, and it has a shaft section 7 and a cup section 8which are integrally formed.

[0005] In particular, six ball-rolling grooves 9 a to 9 f are formed onthe inner wall surface of the cup section 8 so that the ball-rollinggrooves 9 a to 9 f are spaced from each other by predetermined angles inthe circumferential direction (see FIG. 11). The ball-rolling grooves 9a to 9 f are provided for rolling the balls 6 (see FIG. 10). Theball-rolling grooves 9 a to 9 f are provided to extend to the vicinityof the end of the cup section 8 along the inner wall surface of theouter ring member 1 for the barfield-type constant velocity joint (seeFIGS. 11 and 12). On the other hand, a center hole 10 is provided at theend of the shaft section 7 (see FIG. 12).

[0006] The outer ring member 1 for the barfield-type constant velocityjoint is manufactured by cold forging. At first, as shown in FIG. 13A, apretreatment is applied to a workpiece 11 of a columnar material havinga diameter slightly larger than that of the shaft section 7. That is,the workpiece 11 made of carbon steel is subjected to a spheroidizingannealing treatment for depositing cementite in a spherical form in ametal microstructure. Subsequently, a lubricating chemical conversioncoating is formed on the surface thereof by bonderizing. In general coldforging, a coating of zinc phosphate is frequently used as thelubricating chemical conversion coating.

[0007] Subsequently, an unillustrated first forging die is used for aprimary forging (forward extrusion) to the workpiece 11 on which thelubricating chemical conversion coating has been formed. That is, oneend surface of the workpiece 11 is pressed against a cavity which isformed in the first forging die and which has a diameter smaller thanthat of the workpiece 11. Accordingly, the other end surface of theworkpiece 11 is forcibly inserted into the cavity. As a result, as shownin FIG. 13B, a primary forged product 13 is obtained with the shaftsection 7 and a diametrally reduced section 12 having a reduced diameterin a tapered form. The shaft section 7 and a diametrally reduced section12 are formed by the other end of the workpiece 11.

[0008] Subsequently, a secondary forging (upsetting forming) isperformed for the primary forged product 13. Specifically, anunillustrated second forging die is used to successively compress only alarge diameter section 14 of the primary forged product 13 as shown inFIGS. 13C and 13D so that the large diameter section 14 is diametrallyexpanded to obtain a secondary forged product 15.

[0009] The secondary forged product 15 is subjected to a low temperatureannealing treatment for removing any stress or the like and a shot blasttreatment for removing any oxided scale or the like generated during thelow temperature annealing treatment. Further, bonderizing is performedto form a lubricating chemical conversion coating of zinc phosphate orthe like on the outer surface of the second forged product 15.

[0010] Subsequently, a tertiary forging process (backward extrusion) isapplied to the secondary forged product 15 which is arranged in a cavityof an unillustrated third forging die after the respective treatments asdescribed above. The diametrally expanded large diameter section 14 iselongated, ball-rolling grooves 17 a to 17 f are formed on the largediameter section 14, and the cup section 8 is formed.

[0011] That is, an unillustrated punch, which has a projection to formthe ball-rolling grooves 17 a to 17 f, abuts against a central portionof one end surface of the-cup section 8. Subsequently, the end of theshaft section 7 is pressed to displace the secondary forged product 15toward the punch. Accordingly, the secondary forged product 15 iscrushed by the punch while the large diameter section 14 is surroundedby the inner wall of the cavity. Consequently, the large diametersection 14 is elongated, and the ball-rolling grooves 17 a to 17 f,which have shapes corresponding to the shape of the projection of thepunch, are formed on the large diameter section 14. Thus, a tertiaryforged product 18 is obtained as shown in FIG. 13E.

[0012] A low temperature annealing treatment is applied to the tertiaryforged product 18 to soften the tertiary forged product 18. After that,a shot blast treatment is performed again, and a lubricating chemicalconversion coating is formed again by the bonderizing treatment asdescribed above. When various treatments are performed as describedabove, it is possible to avoid cracks which would be otherwise caused bythe tensile stress on the inner surface of the cup section 8 whenironing is performed in the next step.

[0013] Finally, an unillustrated fourth forging die is used to apply theironing (final sizing forming), i.e., a quaternary forging process forfinishing the final product shape. Accordingly, the outer ring member 1for the barfield-type constant velocity joint as the finished product isconsequently obtained (see FIG. 13F).

[0014] As clearly understood from the above, in the conventionalproduction method, it is necessary that various treatment operations,which are complicated and require a long period of time, aresuccessively performed before forging and processing the workpiece 11,the secondary forged product 15, and the tertiary forged product 18. Forthis reason, the entire time required for the production is prolongeduntil the outer ring member 1 for the barfield-type constant velocityjoint is obtained. In other words, in the conventional productionmethod, it is impossible to efficiently manufacture the outer ringmember 1 for the barfield-type constant velocity joint.

[0015] Further, it is inevitably difficult to inexpensively supply theouter ring member 1 for the barfield-type constant velocity joint underthe situation since it is impossible to mass-produce the outer ringmember 1 for the barfield-type constant velocity joint as describedabove.

[0016] An object of the present invention is to provide an outer ringmember for a constant velocity joint and a method of manufacturing themember in which the outer ring member for the constant velocity jointcan be efficiently manufactured by performing continuous forgingmachining without various treatment operations such as low temperatureannealing and bonderizing treatment, and it is possible to reduceproduction cost.

DISCLOSURE OF THE INVENTION

[0017] According to the present invention, an outer ring member for aconstant velocity joint is obtained by forming an intermediate preformedproduct having a cup section with an incomplete shape by pressing adiametrally expanded section of a workpiece without applying a lowtemperature annealing treatment and a lubricating chemical conversioncoating treatment, applying a low temperature annealing treatment, ashot blast treatment, and a lubricating chemical conversion coatingtreatment to the intermediate preformed product, thereafter performingbackward extrusion to the intermediate preformed product, andsubsequently performing ironing.

[0018] In this procedure, the low temperature annealing treatment, theshot blast treatment, and the lubricating chemical conversion coatingtreatment are not performed between the step of the backward extrusionand the step of the ironing.

[0019] The reason why the low temperature annealing treatment, the shotblast treatment, and the formation of the lubricating chemicalconversion coating based on the bonderizing treatment are unnecessaryafter the backward extrusion is that the ironing step is performedbefore causing the work hardening of the formed product which wassubjected to the backward extrusion. That is, in metal material, heat isgenerated during plastic deformation. Therefore, the formed product hasa relatively high temperature and much fluidity immediately after thebackward extrusion is performed. Therefore, it is easy to plasticallydeform the formed product.

[0020] The formed product immediately after backward extrusion begins tocause work hardening in about 2 minutes. Therefore, it is necessary thatthe ironing as the next step is performed as soon as possible.

[0021] As described above, in the present invention, the ironing step issubsequently performed before the formed product obtained by thebackward extrusion causes the work hardening. Therefore, it is possibleto disuse the low temperature annealing treatment, the shot blasttreatment, and the formation of the lubricating chemical conversioncoating. That is, it is preferable that the backward extrusion step andthe ironing step are performed continuously.

[0022] Further, in the present invention, it is possible to improve thestability of quality and the product accuracy of the finished product tobe manufactured in the downstream steps by forming the intermediatepreformed product by using a preforming die before performing thebackward extrusion. In particular, it is possible to improve theaccuracy of grooves formed on the inner wall surface of the cup sectionof the outer ring member for the constant velocity joint as the finishedproduct.

[0023] As clearly understood from the above, the outer ring member forthe constant velocity joint can be efficiently manufactured bycontinuously applying the ironing to the formed product immediatelyafter the backward extrusion to the intermediate preformed product. Thatis, the outer ring member for the constant velocity joint can bemass-produced in a short period of time. Therefore, it is possible tosupply the outer ring member for the constant velocity jointinexpensively.

[0024] It is preferable that the ironing is performed after applying aliquid lubricant to either one of or both of a surface of the formedproduct immediately after performing the backward extrusion step for theintermediate preformed product and a die to be used to perform theironing, for the following reason. The procedure as described abovemakes it possible to avoid occurrence of galling on the formed productor the die for the ironing during the execution of the ironing for theformed product.

[0025] The low temperature annealing herein refers to the operation inwhich the cooling is gradually effected after heating to a temperature,for example, about 680° C. which is lower than the A1 transformationtemperature (temperature at which ferrite and cementite are depositedfrom austenite).

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a flow chart illustrating a method of manufacturing anouter ring member for a constant velocity joint according to anembodiment of the present invention;

[0027]FIGS. 2A to 2G illustrate steps of manufacturing the outer ringmember for the constant velocity joint according to the embodiment ofthe present invention respectively;

[0028]FIG. 3 is, with partial omission, a vertical sectional viewillustrating a state in which an intermediate preformed product isformed by a die apparatus for tertiary forging (die apparatus forpreforming);

[0029]FIG. 4 is a schematic vertical sectional view illustrating aforging die apparatus for executing a quaternary cold forging processstep of the method of manufacturing the outer ring member for theconstant velocity joint according to the embodiment of the presentinvention;

[0030]FIG. 5 is, with partial omission, a vertical sectional viewillustrating a punch of the forging die apparatus shown in FIG. 4;

[0031]FIG. 6 is a magnified vertical sectional view of major parts, inwhich a punch is moved downwardly to form a quaternary forged product;

[0032]FIG. 7 is, with partial cutaway, a sectional view illustrating anouter ring member for a tripod-type constant velocity joint;

[0033]FIG. 8 is a flow chart illustrating a method of manufacturing anouter ring member for a constant velocity joint according to anotherembodiment;

[0034]FIGS. 9A to 9F illustrate steps of manufacturing the outer ringmember for the constant velocity joint according to another embodimentrespectively;

[0035]FIG. 10 shows a schematic arrangement of a driving forcetransmission mechanism comprising four outer ring members for constantvelocity joints which are connected to spline shafts;

[0036]FIG. 11 is a schematic perspective view illustrating the entireouter ring member for the barfield-type constant velocity joint;

[0037]FIG. 12 is, with partial cutaway, a sectional view illustratingthe outer ring member for the barfield-type constant velocity jointshown in FIG. 8; and

[0038]FIGS. 13A to 13F illustrate steps of conventionally forging andprocessing a workpiece respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

[0039] The outer ring member for the constant velocity joint accordingto the present invention will be explained in detail with reference tothe accompanying drawings, as exemplified by preferred embodiments inrelation to the method of manufacturing the member. The constitutivecomponents that are same as the constitutive components shown in FIG. 10to FIGS. 13A to 13F are designated by the same reference numerals, anddetailed explanation thereof will be omitted.

[0040] In a method of manufacturing an outer ring member for a constantvelocity joint according to an embodiment of the present invention, asshown in a flow chart in FIG. 1, the cold forging processes are appliedfive times to a workpiece 11 of a columnar material made of carbonsteel, and the outer ring member 1 for the barfield-type constantvelocity joint (see FIGS. 11 and 12) is finally manufactured.

[0041] Respective steps of the production method according to theembodiment of the present invention are shown in FIGS. 2A to 2G. In theconventional production method, the low temperature annealing treatmentand the lubricating chemical conversion coating treatment are appliedbetween the tertiary cold forging process and the quaternary coldforging process (see FIGS. 13E and 13F). In contrast, the productionmethod according to the embodiment of the present invention differs inthat these treatments are omitted between the quaternary cold forgingprocess and the quinary cold forging process (see FIGS. 2F and 2G). Inother words, in the production method according to the embodiment of thepresent invention, the quinary cold forging process is continuouslyapplied to the quaternary forged product 24 to which the quaternary coldforging process has been applied, without performing various treatmentsincluding the low temperature annealing treatment and the lubricatingchemical conversion coating treatment.

[0042] Further, the embodiment of the present invention differs from theconventional production method in that the intermediate preformedproduct 16 as a tertiary forged product is formed between the secondaryforged product 15 and the quaternary forged product 24 (see FIG. 2E).

[0043] At first, in a first preparatory step Ssub1, a spheroidizingannealing treatment is applied to a workpiece 11 (see FIG. 2A) cut intoa columnar material having a predetermined length. Accordingly, theworkpiece 11 is softened, and it is easy to perform the primary toquinary cold forging processes to be performed thereafter.

[0044] In a second preparatory step Ssub2, a lubricating chemicalconversion coating is formed on the workpiece 11. That is, thelubricating chemical conversion coating of zinc phosphate or the like isformed on the surface of the workpiece 11 by a bonderizing treatment togive the lubricating property to the surface. Specifically, thelubricating chemical conversion coating may be formed by immersing theworkpiece 11 in a solvent dissolved with zinc phosphate or the like asdescribed above for a predetermined period of time.

[0045] Subsequently, in a primary cold forging process step S1, theforward extrusion is applied to the workpiece 11 on which thelubricating chemical conversion coating has been formed. That is, theworkpiece 11 is charged into a workpiece holder of a first forging diehaving an unillustrated cavity for forming the shaft section. The cavityfor forming the shaft section has a diameter which is smaller than thatof the workpiece 11. Further, a tapered surface is provided between theworkpiece holder and the cavity for forming the shaft section.

[0046] Starting from this state, one end surface of the workpiece 11 ispressed toward the cavity for forming the shaft section. In accordancewith this pressing operation, the other end surface portion of theworkpiece 11 is forcibly inserted into the cavity for forming the shaftsection. As a result, a primary forged product 13 (see FIG. 2B) isobtained, which is formed with a shaft section 7 and a diametrallyreduced section 12 having a reduced diameter in a tapered form on theside of the other end surface. The portion of the workpiece 11, which ischarged into the workpiece holder, scarcely undergoes plasticdeformation. Therefore, the primary forged product 13 has a largediameter section 14 with its diameter being a size corresponding to thediameter of the workpiece 11.

[0047] Subsequently, in a secondary cold forging process step S2, theupsetting is performed for the primary forged product 13. That is, theprimary forged product 13 is charged into a cavity of an unillustratedsecond forging die. During this process, the shaft section 7 is insertedinto a shaft section holder provided for the second forging die.

[0048] The large diameter section 14 of the primary forged product 13 ispressed and crushed with a punch while the end of the shaft section 7inserted into the shaft section holder is supported with a holdingstopper member. The large diameter section 14 is compressed andsubjected to the expansion of the diameter thereof in accordance withthe crushing. Thus, a secondary forged product 15 (see FIG. 2D) isobtained.

[0049] Subsequently, in a tertiary cold forging process step S3, theforward extrusion is applied to the large diameter section 14 of thesecondary forged product 15 as preforming to form an intermediatepreformed product 16 as a tertiary forged product (see FIG. 2E).

[0050] That is, as shown in FIG. 3, a third forging die (preforming die)19 is used to press with a punch 20 the large diameter section 14 of thesecondary forged product 15 charged into a cavity so that the largediameter section 14 is plastically deformed to form the intermediatepreformed product 16 (tertiary forged product) having a cup section 21with an incomplete shape as compared with the cup section 8 of thefinished product.

[0051] As shown in FIG. 2E, the cup section 21 having the incompleteshape as described above is provided with a recess 22 which isrelatively shallow and which has a circular arc-shaped cross sectionformed by being pressed by the end of the punch 20, and ball-rollinggrooves 23 a to 23 f which are formed on the inner wall surface of therecess 22 and which have incomplete shapes as compared with theball-rolling grooves 9 a to 9 f formed on the finished product.

[0052] The bottom portion of the cup section 21 having the incompleteshape is relatively thick-walled as compared with the finished productas described later on, and is connected to the shaft section 7 of theintermediate preformed product 16. The dimension of the cup section 21from the top to the bottom surface is smaller than the dimension of thecup section 8 of the finished product.

[0053] In this procedure, the intermediate preformed product 16(tertiary forged product) is formed by using the preforming die, andthus it is possible to improve the stability of quality and the productaccuracy of the finished product formed in the downstream steps.

[0054] The low temperature annealing for removing stress from theintermediate preformed product 16, the shot blast treatment for removingoxided scale or the like generated during the low temperature annealing,and the formation of the lubricating chemical conversion coating of zincphosphate or the like on the outer surface of the intermediate preformedproduct 16 by the bonderizing treatment are performed in third to fifthpreparatory steps Ssub3, Ssub4, and Ssub5 respectively after completingthe tertiary cold forging process step S3. When the various treatmentsas described above are performed, it is easy to plastically deform theintermediate preformed product 16 (tertiary forged product).

[0055] After that, a forging die apparatus (fourth forging die) 30 shownin FIG. 4 is used to perform a quaternary cold forging process step S4.

[0056] The structure of the forging die apparatus 30 will now beschematically explained.

[0057] The forging die apparatus 30 has a first die plate 32 and asecond die plate 34. A forcible insertion ring 36, which isthick-walled, is fixed on the first die plate 32 by an unillustratedfixing member.

[0058] An insert member 38 has a cylindrical shape, and is internallyfitted to a hole of the forcible insertion ring 36. The outer diameterof the insert member 38 is slightly larger than the inner diameter ofthe forcible insertion ring 36. That is, the insert member 38 is fittedinto the hole of the forcible insertion ring 36 by interference fit.

[0059] Further, a lower die 40 has a short size in the axial directionas compared with the insert member 38, and is arranged in the insertmember 38. An upper die 42 is joined onto the lower die 40 so that theupper end thereof is flush with the upper end of the insert member 38.In particular, a shaft insert section 44 is provided in the lower die 40in order to insert the shaft section 7 of the intermediate preformedproduct 16 (tertiary forged product).

[0060] A through-hole 54 is provided at a position disposed verticallydownwardly from the shaft insert section 44, and is communicated with ahole 52 formed in the first die plate 32. A knockout pin 55 is arrangedin the through-hole 54, and is movable upwardly or downwardly therein.

[0061] On the other hand, the upper die 42 is provided with a cupsection-forming cavity 56 in order that the cup section 21 of theintermediate preformed product 16 (tertiary forged product) having theincomplete shape is formed into the cup section 8 having the completeshape (see FIG. 11). It is a matter of course that the diameter of thecup section-forming cavity 56 is set to be larger than that of the shaftinsert section 44.

[0062] A first ring member 58 is joined to the upper end surface of theupper die 42. Further, a second ring member 60 is joined to the upperend surface of the insert member 38, and is externally fitted to thefirst ring member 58. Further, a third ring member 62 is joined to anannular recess provided on the forcible insertion ring 36, and isexternally fitted to the second ring member 60.

[0063] In this arrangement, when the third ring member 62 is fastened tothe forcible insertion ring 36 so that the second ring member 60 isexternally fitted, a tapered surface 62 a formed on the third ringmember 62 makes sliding contact with a reverse tapered surface 60 aformed on the second ring member 60. As a result, the force is exertedto press the first ring member 58 and the second ring member 60 in thedownward direction.

[0064] On the other hand, a hole 64 is formed in the first ring member58. A punch 66 is inserted into the hole 64. A guide sleeve 68 of acylindrical member made of metal is externally fitted to the sidecircumferential wall of the punch 66 in order that the punch 66 issmoothly operated and moved upwardly or downwardly. Therefore, the guidesleeve 68 is interposed between the first ring member 58 and the punch66.

[0065] In this arrangement, as shown in FIG. 5, six striped ridges 70 ato 70 f, which are spaced from each other by 600 in the circumferentialdirection and which extend by predetermined lengths in the axialdirection of the punch 66, are provided on the outer circumference ofthe end of the punch 66. Each of the striped ridges 70 a to 70 f has afirst straight portion-forming region 72, a circular arc-shapedportion-forming region 74, and a second straight portion-forming region76 in this order from the end of the punch 66. As shown in FIG. 6, theball-rolling grooves 17 a to 17 f having the complete shapes are formedon the cup section 8 of the quaternary forged product 24 by the stripedridges 70 a to 70 f. The ironing is performed for the cup section 8,especially for the ball-rolling grooves 17 a to 17 f in a quinary coldforging process step S5 as described later on. Thus, the ball-rollinggrooves 9 a to 9 f (see FIGS. 11 and 12) are formed, in which the shapeand size accuracies are further improved.

[0066] The punch 66 is movable upwardly or downwardly by anunillustrated machine press. That is, a ram (not shown) of the machinepress is connected with a vertically movable member 82 which isdisplaceable in the upward or downward direction together with the ram(see FIG. 4). The punch 66 is fixed to the vertically movable member 82by a jig 84.

[0067] The quaternary cold forging process, i.e., the backward extrusionis performed as follows for the intermediate preformed product 16(tertiary forged product) with the shaft section 7 inserted into theshaft insert section 44 of the forging die apparatus 30 constructed asdescribed above. The end surface of the shaft section 7 abuts againstthe end surface of the knockout pin 55 when inserted into the shaftinsert section 44.

[0068] At first, the vertically movable member 82 connected to the ramof the machine press is moved downwardly by the machine press. The punch66 is moved downwardly to follow this operation, and the punch 66finally abuts against the recess 22 of the cup section 21 of theintermediate preformed product 16 (tertiary forged product).

[0069] When the punch 66 is further moved downwardly, the ball-rollinggrooves 17 a to 17 f, which are directed in the axial direction of theintermediate preformed product 16 (tertiary forged product), are formedon the inner wall surface of the cup section 8 by the striped ridges 70a to 70 f of the punch 66. That is, the ball-rolling grooves 17 a to 17f having the complete shapes, which include straight portions, circulararc-shaped portions, and straight portions corresponding to the firststraight portion-forming regions 72, the circular arc-shapedportion-forming regions 74, and the second straight portion-formingregions 76 of the striped ridges 70 a to 70 f, are provided on the cupsection 8.

[0070] Simultaneously, as shown in FIG. 6, one end surface of the cupsection 21 having the incomplete shape, which is crushed by the punch66, enters the space between the side circumferential wall of the punch66 and the cup section-forming cavity 56, while being elongated inaccordance with the plastic flow. Accordingly, the cup section 8, whichhas the complete shape and which is relatively thick-walled and long, isformed.

[0071] It goes without saying that the load is applied so that theknockout pin 55 is not moved downwardly during this process. That is,the intermediate preformed product 16 (tertiary forged product) is notdisplaced during the formation of the cup section 8 and the ball-rollinggrooves 17 a to 17 f.

[0072] After that, the punch 66 is moved upwardly together with the ramand the vertically movable member 82 by the machine press so that thepunch 66 is disengaged from the first ring member 58, and the knockoutpin 55 is moved upwardly. Accordingly, the quaternary forged product 24(see FIG. 2F) is exposed.

[0073] Metal material ordinarily has a property that heat is generatedduring the plastic flow. Therefore, the quaternary forged product 24 hasa relatively high temperature immediately after the plastic deformation.If the quaternary forged product 24 is left and cooled in this state,then the work hardening is caused, and the hardness and the strength areincreased. That is, it is difficult to effect the plastic deformationagain.

[0074] Accordingly, in the embodiment of the present invention, thequinary cold forging process is continuously applied to the quaternaryforged product 24 having the relatively high temperature immediatelyafter performing the quaternary cold forging process step S4. In thisprocedure, the quaternary forged product 24 can be plastically deformedwith ease, because the operation is performed before the quaternaryforged product 24 causes the work hardening.

[0075] Further, it is unnecessary to perform the low temperatureannealing for softening the quaternary forged product 24, because it iseasy to effect the plastic deformation. Therefore, no oxided scaleappears, and hence it is also unnecessary to perform the shot blasttreatment. Further, the material which causes the plastic deformationwith ease, in other words, the material which plastically flows withease makes lubrication relatively satisfactorily with respect to aforging die. Therefore, it is also unnecessary to form the lubricatingchemical conversion coating.

[0076] That is, when the quinary cold forging process step S5 issubsequently or continuously performed immediately after the quaternarycold forging process step S4, it is unnecessary to perform the lowtemperature annealing treatment, the shot blast treatment, and theformation of the lubricating chemical conversion coating based on thebonderizing treatment which were performed between the tertiary forgingprocess and the quaternary forging process in the conventionalproduction method. Accordingly, it is possible to efficientlymanufacture the outer ring member 1 for the barfield-type constantvelocity joint. In other words, the outer ring member 1 for thebarfield-type constant velocity joint can be mass-produced in a shortperiod of time. Therefore, it is possible to supply the outer ringmember 1 for the barfield-type constant velocity joint inexpensively.

[0077] As shown in FIG. 1, before the quinary cold forging process stepS5, a liquid lubricant is applied to at least one of the surface of thequaternary forged product 24 and a fifth forging die (not shown) in asixth preparatory step Ssub6. Accordingly, it is possible to avoid theoccurrence of galling on the quaternary forged product 24 or the fifthforging die during the execution of the quinary cold forging processstep S5. A liquid lubricant which is commonly known may be used as theliquid lubricant.

[0078] In the quinary cold forging process step S5, the unillustratedfifth forging die is used to apply the ironing (final sizing forming) tothe quaternary forged product 24 in order that the cup section 8 isfinished to have the final product shape. That is, the cup section 8 isprocessed so that the wall thickness of the cup section 8 and the depthsof the ball-rolling grooves 17 a to 17 f have predetermined sizes.Accordingly, the outer ring member 1 (see FIGS. 2G, 11, and 12) for thebarfield-type constant velocity joint is consequently obtained as thefinished product which is provided with the size accuracy of the cupsection 8 including the shapes of, for example, the ball-rolling grooves9 a to 9 f. Simultaneously, the center hole 10 (see FIG. 12) is formedin the shaft section 7 by a projection (not shown) provided at the endof a knockout pin (not shown) of the fifth forging die.

[0079] The plastic deformation of the quaternary forged product 24 isextremely minute in the step S5. Therefore, even when the step S5 isperformed without applying the low temperature annealing treatment, theshot blast treatment, and the lubricating chemical conversion coatingtreatment, the inner surface of the cup section 8 is prevented from theoccurrence of cracks which would be otherwise caused by the action ofthe tensile stress during the forging process.

[0080] According to the production method concerning the embodiment ofthe present invention, the intermediate preformed product 16 is formedas the tertiary forged product before executing the quaternary coldforging process step S4. Thus, it is possible to improve the stabilityof quality and the accuracy of the finished product.

[0081] In other words, even if the shape of the cup section 21 isincomplete in the intermediate preformed product 16, when the cup shapeis formed to have the curved recess 22 and the partial ball-rollinggrooves 23 a to 23 f, then the ball-rolling grooves 17 a to 17 f can beformed easily and accurately on the inner wall surface of the cupsection 8 in the quaternary cold forging process step, and it ispossible to further improve the formability of the ball-rolling grooves17 a to 17 f.

[0082] Further, according to the production method concerning theembodiment of the present invention, the quinary cold forging processstep S5 can be performed without performing the low temperatureannealing treatment, the shot blast treatment, and the formation of thelubricating chemical conversion coating based on the bonderizingtreatment after the quaternary cold forging process step S4.Accordingly, it is possible to efficiently manufacture the outer ringmember 1 for the barfield-type constant velocity joint. Therefore, it ispossible to provide the outer ring member 1 for the barfield-typeconstant velocity joint inexpensively.

[0083] Further, according to the production method concerning theembodiment of the present invention, the low temperature annealingtreatment and the lubricating chemical conversion coating treatment areapplied only once after the formation of the intermediate preformedproduct 16. Accordingly, it is possible to continuously perform thebackward extrusion as the quaternary cold forging process step S4 andthe ironing as the quinary cold forging process step S5.

[0084] Further, according to the production method concerning theembodiment of the present invention, it is unnecessary to performvarious complicated and troublesome treatments such as the lowtemperature annealing treatment, the shot blast treatment, and thebonderizing treatment that were performed conventionally between thequaternary cold forging process step S4 for performing the backwardextrusion and the quinary cold forging process step S5 for performingthe ironing. Thus, it is possible to reduce the labor of the operatorand various costs.

[0085] That is, the operation is extremely laborious for the operatorsuch that a plurality of formed products of outer ring members forconstant velocity joints of heavy materials are imported into anunillustrated annealing furnace or the like to perform the lowtemperature annealing treatment, the formed products are thereafterexported from the unillustrated annealing furnace, the formed productsare transported to an unillustrated shot blast apparatus to perform theshot blast treatment, and an unillustrated bonderizing lubricationtreatment apparatus is used to successively perform the bonderizingtreatment. Further, the operation as described above requires variouscosts such as supplies for treatment materials and expenses foroperating the equipment required for the various treatments. Further,the labor load is heavily burdened in the transport operation or thelike, because the workpiece is heavy in weight.

[0086] The embodiment described above is illustrative of the case inwhich the outer ring member 1 for the barfield-type constant velocityjoint is manufactured. However, there is no special limitation thereto.It is also possible to manufacture an outer ring member 2 for atripod-type constant velocity joint having three track grooves 90 a to90 c formed in a cup section 8 as shown in FIG. 7.

[0087] Next, a production method according to another embodiment isshown in FIGS. 8 and 9.

[0088] The production method according to another embodiment shown in aflow chart in FIG. 8 differs in that the step of forming theintermediate preformed product 16 (see the step S3 in FIG. 3) is omittedfrom the production method according to the embodiment described aboveshown in the flow chart in FIG. 1. All of the other steps are identical.

[0089] That is, the production method according to another embodiment ischaracterized in that the tertiary cold forging process step (see thestep S13 in FIG. 8) is performed by using the forging die apparatus 30shown in FIG. 4 without forming the intermediate preformed product 16 asthe tertiary forged product, and the quaternary cold forging processstep (see the step S14 in FIG. 8) including the ironing is performedcontinuously to the tertiary cold forging process step without applyingthe low temperature annealing treatment and the lubricating chemicalconversion coating treatment respectively.

[0090] As a result, the production steps are further simplified in theproduction method according to another embodiment, and thus it ispossible to shorten the production time and reduce the production cost.The other function and effect are the same as those of the productionmethod according to the embodiment described above, and hence anydetailed explanation thereof is omitted.

INDUSTRIAL APPLICABILITY

[0091] As described above, according to the present invention, thediametrally expanded section of the workpiece is pressed to form theintermediate preformed product having the cup section with theincomplete shape without applying the low temperature annealingtreatment and the lubricating chemical conversion coating treatment. Thelow temperature annealing treatment, the shot blast treatment, and thelubricating chemical conversion coating treatment are applied to theintermediate preformed product. After that, the backward extrusion isperformed for the intermediate preformed product, and the ironing isperformed subsequently. Thus, it is possible to omit the low temperatureannealing treatment, the shot blast treatment, and the lubricatingchemical conversion coating treatment between the backward extrusionstep and the ironing step.

[0092] That is, the ironing is continuously applied before causing thework hardening after the backward extrusion to the intermediatepreformed product. Accordingly, it is unnecessary to perform the lowtemperature annealing treatment, the shot blast treatment, and theformation of the lubricating chemical conversion coating between thebackward extrusion step and the ironing step. Therefore, it is possibleto efficiently manufacture the outer ring member for the constantvelocity joint, and it is possible to reduce the production cost.

[0093] Further, according to the present invention, the intermediatepreformed product is formed before performing the backward extrusion.Accordingly, it is possible to improve the stability of quality and theproduct accuracy of the finished product.

1. An outer ring member for a constant velocity joint obtained by:forming a shaft section (7) by forward extrusion to a workpiece (11)having a surface with a lubricating chemical conversion coating; forminga diametrally expanded section (14) by upsetting a portion of saidworkpiece (11) except for said shaft section (7); forming thereafter anintermediate preformed product (16) having a cup section (21) with anincomplete shape by pressing said diametrally expanded section (14)without a low temperature annealing treatment and a lubricating chemicalconversion coating treatment; applying a low temperature annealingtreatment and a lubricating chemical conversion coating treatment tosaid intermediate preformed product (16) and thereafter forming a formedproduct (24) having a cup section (8) provided with grooves (17 a to 17f) by applying backward extrusion to said intermediate preformed product(16); and subsequently ironing said formed product (24) before causingwork hardening in said formed product (24) without applying a lowtemperature annealing treatment and a lubricating chemical conversioncoating treatment to said formed product (24).
 2. An outer ring memberfor a constant velocity joint comprising: a shaft section (7) formed byforward extrusion to a workpiece (11) having a surface with alubricating chemical conversion coating; and a cup section (8) formed bya pressing force to a diametrally expanded section (14), saiddiametrally expanded section (14) formed by upsetting a portion exceptfor said shaft section (7), said shaft section (7) being extended bysaid pressing force, grooves (17 a to 17 f) being formed on saiddiametrally expanded section (14) by said pressing force, wherein afterforming said cup section (8), said workpiece (24) is ironed before workhardening in said workpiece (24), without applying a low temperatureannealing treatment and a lubricating chemical conversion coatingtreatment to said workpiece (24).
 3. A method of manufacturing an outerring member for a constant velocity joint having a shaft section and acup section integrally, said method comprising the steps of: formingsaid shaft section (7) by forward extrusion to a workpiece (11) having asurface with a lubricating chemical conversion coating; forming adiametrally expanded section (14) by upsetting a portion of saidworkpiece (11) except for said shaft section (7), and then forming anintermediate preformed product (16) having a cup section (21) with anincomplete shape by pressing said diametrally expanded section (14)without a low temperature annealing treatment and a lubricating chemicalconversion coating treatment; applying a low temperature annealingtreatment and a lubricating chemical conversion coating treatment tosaid intermediate preformed product (16) and thereafter forming a formedproduct (24) having said cup section (8) provided with grooves (17 a to17 f) by backward extrusion to said intermediate preformed product (16);and subsequently ironing said formed product (24) before work hardeningin said formed product (24) without applying a low temperature annealingtreatment and a lubricating chemical conversion coating treatment tosaid formed product (24).
 4. The method of manufacturing said outer ringmember for said constant velocity joint according to claim 3, wherein aliquid lubricant is applied to any one of or both of a surface of saidformed product (24) and a die into which said formed product (24) ischarged, before said ironing.
 5. A method of manufacturing an outer ringmember for a constant velocity joint having a shaft section and a cupsection integrally, said method comprising the steps of: forming saidshaft section (7) by forward extrusion to a workpiece (11) having asurface with a lubricating chemical conversion coating; forming adiametrally expanded section (14) on said workpiece (11) by upsetting aportion except for said shaft section (7); forming said cup section (8)by applying a pressing force to said diametrally expanded section (14)to elongate said diametrally expanded section (14) and provide grooves(17 a to 17 f) on said diametrally expanded section (14); and formingsaid outer ring member (1) for said constant velocity joint by ironingsaid workpiece (24) formed with said shaft section (7) and said cupsection (8), wherein after forming said cup section (8) by providingsaid grooves (17 a to 17 f) on said diametrally expanded section (14),said workpiece (24) is ironed before work hardening in said workpiece(24) without applying a low temperature annealing treatment and alubricating chemical conversion coating treatment to said workpiece(24).
 6. The method of manufacturing said outer ring member for saidconstant velocity joint according to claim 5, wherein a liquid lubricantis applied to any one of or both of a surface of said workpiece (24) anda die into which said workpiece (24) is charged before said ironing.